In recent years, the concrete industry has been deluged with a plethora of exotic additives for concrete. These additives include air entraining agents, air detraining agents, accelerants, alkali reactivity reducers, superplasticizers, pumping aids, water reducing admixtures, corrosion inhibitors, permeability reducers and fibers, to name a few. When utilizing these additives, it is important, and often critical, to know the volume of concrete into which the additive is to be added. This is particularly critical when adding set retarders or delayed setting admixtures.
In a typical concrete application, the concrete mixing truck will return to the concrete mixing yard with some wet concrete still in the drum. In the past, this volume had been washed out directly into a landfill and wasted. Unfortunately, this is not an environmentally friendly practice. This type of wasting has a deleterious effect on ground water. Accordingly, concrete vendors would like to recover their unused cement and use it the next day. Unfortunately, mechanical reclaiming systems require a large capital investment initially and a lot of ongoing maintenance to keep them operational. As a result, many products have entered the market for use as set retarders. These products include lignosulfonates, hydroxylated carboxylic acids, lignin, borax, gluconic, tartaric and other organic acids and their corresponding salts, and certain carbohydrates. Unfortunately, these materials require the user to know how much concrete remains in the truck to a fairly accurate degree. If too little set retarder is added to the concrete, the concrete will set up overnight and have to be chiseled out. If too much set retarder is added, the resulting concrete may never set properly. Unfortunately, it has proved to be increasingly difficult to provide a simple determination for volume in a concrete truck.
At present, the only accurate means of determining the volume of concrete in the truck to weight the truck empty, and weigh it upon its return from the job site. The gravimetric determination is then converted to volume with a simple density conversion factor. Unfortunately, many small concrete vendors do not have this capability and furthermore, other factors, like gasoline usage and water content in the wash tank can inadvertently affect the weight change.
Some have proposed taking comparative photographs of the inside of the mixing truck at different concrete volume levels and using those to determine the volume. This method has proved to be unreliable.
Accordingly, it is an object of the present invention to provide a simple, accurate method for determining the volume of concrete in a concrete mixer.